MUNICH — The air in Beijing, Moscow and Cairo is full of emissions and noxious matter that people can see, smell and sometimes even taste. And they are in fact deadly, leading every year to premature deaths, according to new research by the Max Planck Institute for Chemistry in Mainz, Germany.

The numbers of deaths due to lung and heart diseases, cancer and strokes are alarming: Per 100,000 citizens, there are 126 premature deaths in Beijing, 58 in Moscow and 48 in Cairo.

"Especially in Asian cities, the volume of fine dust particulates is alarmingly high," says Jos Lelieveld, director of the Max Planck Institute. "We even had to adapt our computer models, created for European and American metropolises, to the extreme concentration in Asia."

Of the 3.3 million people who died in 2010 from air pollution, 1.4 million were Chinese, Lelieveld's results show. And his overall numbers are confirmed by other research. In March, North American researchers calculated 3.2 million premature deaths in 2014 due to air pollution, and the World Health Organization (WHO) estimated 3.7 million for last year.

What's new about Lelieveld's study is that it differentiates death rates according to particulate matter. In Cairo, the culprit is desert dust. In Moscow, the offending emissions come from agriculture, and in Beijing from fire used in cooking and heating. The noxious substances don't just come from the cities, but also from the surrounding areas.

With a global computer model, Lelieveld's team was able to reconstruct the dispersion of substances in the atmosphere through the wind.

In particular, agriculture's contribution to pollution surprised the researchers. "We are talking about ammonia and other nitrogen emissions that are generated during the work with animals," Lelieveld says. In Europe, Turkey and the eastern United States, agriculture is the most serious source of particulate matter.

From a global point of view, the burning of wood and cow dung represents a much bigger problem, particularly in Asia's populous countries. The smoke is directly responsible for a million premature deaths all over the world, according to the scientist's calculations. But smoke also contributes to the lion's share of 3.5 million deaths every year, because the air in people's homes is polluted. In many Asian countries, coal-fired power plants are the second biggest source of particulate matter.

The worst offender

China has 101 premature deaths due to air pollution for every 100,000 of its citizens — a ratio that drives up the global average. If you leave out China, the average number of deaths globally drops from 48 to 36. Germany has 42 per 100,000, about half caused by agricultural emissions and a fifth by traffic emissions, placing Germany 12^th overall.

"It's an interesting study, principally because of the consideration of different sources of particulate matter," says Annette Peters from the Helmholtz-Zentrum in Munich. But she questions the assumption that agriculture is a major problem in countries like Germany. "Scientists agree that there is a large amount of those particles, but it remains unclear if, next to combustion processes, they have a comparable impact on health."

Lelieveld and his team are investigating this too. To quantify this objection, they have assumed that smoke particles would be five times as toxic as agricultural emissions. This would reverse the order of sources for Germany's premature deaths: Traffic emissions would become the number one cause of death whereas agriculture's impact would be cut in half.

"This study is potentially crucial for public health protection," says the University of California's Michael Jerrett. "A million people can be saved each year. The fight against particulate matter has to be approached differently from country to country. In China, protection from exposure to tobacco smoke has no measureable effect. But it is much more important in countries where other problems have already been eliminated."